This invention relates generally to apparatus for removing copy medium from a roll member, and, more particularly, to means for facilitating the removal of a copy sheet from a fuser roll apparatus.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, for example, as by the use of heat and pressure.
It is known to use various combinations of heated rollers and pressure roller and combinations thereof as the fusing mechanism. With these roller configurations, the toner image sometimes forms a strong bond between the fuser roll surface and the copy sheet. It may therefore, at some point be necessary to separate the fused copy sheet from the fuser roller. Various mechanical stripping devices are known from the prior art. In U.S. Pat. No. 4,336,992, assigned to Xerox Corporation, a rotatable flexible stripper finger structure is used to strip copy sheets from a heated pressure roller assembly. U.S. Pat. No. 4,264,181 discloses a heated roll/backup roll fuser arrangement with a plurality of chisel fingers 30 separating copy sheets from the heated roller. U.S. Pat. No. 4,156,524, also assigned to Xerox Corporation, discloses an elongated stripping blade member which is used to strip the copy sheet from the heated fuser roll surface.
U.S. Pat. No. 970,441 to Gammeter describes a paper stripping device for stripping paper from a printing couple. A flexible paper strip is held by a metal clip which is adjustably mountable onto a printing-press. In the event that the strip is improperly placed, it may be drawn out of its clip and fed through the press, thus preventing harm to the printing machine.
U.S. Pat. No. 2,211,766 to Brown, Jr. describes a stripping device for removing sheets from a drum of a printing press. The stripper comprises a plate bent to form a plurality of creased portions which provide closely spaced sheet-contacting surfaces. The stripper is adapted to lie close to a printing member and the sheet-contacting surfaces are sufficiently narrow to avoid collection or smearing of the ink.
U.S. Pat. No. 3,936,045 to Ariyama describes a sheet pick-off member comprising a thin strip conforming to the configuration of a photoconductive drum. A narrow strip of copy material extends along a side of the drum and moves over the stripping member as the length of the copy material moves under a transfer corona. A projecting portion of the thin strip then moves a leading corner of the copy material away from the drum and into the nip of a turn roll and a rubber belt which then carry the sheet away from the photoconductive drum.
These prior art stripper mechanisms can be generally characterized as providing a wedge surface with a very sharp point in contact with the roll member. They present a relatively smooth sloping surface upon which the separated copy sheet glides for some distance before separating completely.
It has been found that, for certain applications, these prior art systems are unsatisfactory to effect desired sheet removal. For example, for fusing systems used in wide document copiers such as the Xerox 2510 the fuser roll has a cylindrical form which may exceed 36 inches in length. For rollers of this length, it has proved difficult to maintain machining tolerances to completely eliminate roller eccentricity during rotation. In other words, the rollers have some degree of wobble during rotation. For the prior art wedge sharp-edged rollers, even a slight eccentricity is sufficient to cause gouging of the roll surface by the rigidly mounted fingers. According to one aspect of the invention, the stripper fingers are constructed of a thin sheet metal material. The left-off (finger) portion has a generally curved surface and is positioned so as to flexibly conform to the fuser roll surface at the pickoff angle. The fingers portion conforms to the roller surface even through a wobble excursion.
A second problem with the fuser systems of wide document copiers is that of contamination usually incurred with using acetate sheets as the record medium. The acetate sheets have a tendency to leave an oil deposition on any frictionally engaging surface. Prior art stripper fingers presenting a relatively smooth surface to the copy sheet being removed tend towards an oil deposition buildup on the finger surface. This buildup, in turn, contaminates subsequent copies. As another aspect of the present invention, the stripper fingers are provided with increasingly elevated edges which carry the copy sheets away from the finger surface. Since the copy sheets are riding on very thin edges, the oil deposition problem is minimized. It has been found that the raised edges also increase the beam strength of the fingers, enabling the fingers to separate relatively heavy stack copy paper without deforming. More particularly, the invention relates to a sheet separation mechanism for effecting removal of a record medium from a roll member, said mechanism comprising:
a plurality of flexible elongated stripping fingers positioned proximate and along the width of said roll member surface, said stripping fingers having a generally curved flexible tip portion adapted to effect initial separation of the record medium from the roll member, each finger having at least one rigid edge segment protruding upward from said finger and adapted to gradually guide the record medium away from the stripping finger surface.